Many older adults have difficulty understanding speech in complex and demanding environments typical of everyday listening. Using typical laboratory outcome measures, speech-understanding difficulties of older hearing-impaired subjects are accounted for primarily by reductions in speech audibility due to elevated thresholds. Given the importance of speech audibility, amplification provided by a hearing aid should restore important speech information and provide significant benefit to communication. Nevertheless, only a fraction of older adults who could derive benefit from amplification own hearing aids and use them regularly. The lack of success and satisfaction with hearing aids suggests that a fundamental change in direction is needed. The current understanding of communication needs is based on conclusions drawn from performance obtained in highly unrealistic conditions. The design and fitting of communication aids for older adults should be guided by their listening performance in complex and demanding environments that contain the acoustic and perceptual variability inherent in everyday situations. Thus, in Project 2, a series of experiments is planned to address key questions concerning the use of speech information by older adults as delivered and perceived in realistic environments. Aim 2.1 tests the hypothesis that the audibility of high-frequency interaural difference cues underlies the ability to benefit from spatial separation of speech and noise sources. Aim 2.2 tests the hypothesis that rate of recovery from prior stimulation, especially at higher frequencies, underlies the ability to benefit from envelope fluctuations in speech-like noise. Aim 2.3 tests the hypothesis that age-related changes in auditory selective attention increase the detrimental effects of stimulus uncertainty. A long-term goal is to extend our general understanding of mechanisms that account for reduced speech understanding in noise by older adults and thus enhance benefit derived from amplification.